Just a thought, perhaps expressed in some other thread...

I always thought the song was a train song, and the "6 white horses" is a conflation of the images of 1)the 3 pairs of big wheels on a steam locomotive; and 2)the clouds of white steam billowing from the stack.

I don't have a clue about the pajamas, though I've always heard/sung it as "silk pajamas" which would go with the wealth idea.

And someone in my family (I suspect my dad though maybe my mother's father) added "We'll be eatin' buckwheat flapjacks when she comes" which can be a bit of a tongue-twister if the banjo-player has kicked off the tune a mite faster than you're used to...

just my $0.02, your mileage may vary...

V